Method for mounting an electronic component on a substrate

ABSTRACT

This invention proposes a manufacturing process for a transponder in the form of a card or a label able to resist to flexions or twisting without interrupting the connections of the electronic components. The process of assembling at least one electronic component including sensibly flat conductive areas that are connected to conductive tracks placed on the surface of a generally flat substrate comprises the steps of placing the substrate on a work surface, the face including conductive tracks being oriented upwards, placing the electronic component into a cavity of the substrate situated in a zone including the conductive tracks, the conductive areas of the component coming into contact with the corresponding tracks of the substrate and applying a layer of insulating material which extends at once on the electronic component and at least on a substrate zone surrounding said component. This process implies that the contact between the conductive areas of the electronic component and the conductive tracks of the substrate realizes an electric connection ensured by the pressure of application of the insulating material layer on the electronic component.

This invention relates to an assembly process of an electronic componenton an insulating support called a substrate that includes a plurality ofconductive tracks. This process can be applied during the manufacturingof transponders in the form of a card or an electronic label whichthickness is generally low.

Electronic label is understood to mean an assembly comprising at leastone insulating support, an antenna and an electronic component, usuallya chip. The card or electronic label made using the process according tothe invention is found in numerous applications as a mean ofidentification, control or payment.

The subject of this invention is particularly focused on the assembly ofat least one electronic component on the substrate of a thin card orlabel. An electronic component is an element such as: a chip, acapacity, a resistance, a diode, a fuse, a battery, a display, or alsoan assembly comprising a coated chip provided with contact areas.

Cards or labels are known by those skilled in the art where componentsare mounted on a substrate, on which conductive tracks and connectionareas (usually in copper) are engraved. The components are usuallybonded, then their contacts are welded onto the tracks or onto theconductive connection areas of the substrate. The electric contactbetween the connection areas of the component and those of the substrateis achieved by means such as: bonding with a conductive glue, welding bymeans of ultrasounds, welding by means of a hot applied tin-based alloy.

Cards are also known that are provided with components whose contactsare provided with claws or spikes (bumps) which are embedded by pressinginto the engraved connection areas of the substrate. The documentWO0055808 describes the production of a connection between a chip andthe contact areas of an antenna by hot lamination. The contacts of thechip include bumps that are embedded in the conductive material of theantenna's connection area producing a deformation in these areas.

The connections of components on substrate conductors can also beobtained by means of conductive wires welded on one hand on a substrateconductor and on the other hand on a conductive area of the component.

In order to protect the components and the circuits wired in this way,an epoxy resin can be cast on all or part of the substrate surface inorder to coat the circuit components assembly. According to anotherembodiment, an insulating sheet is laminated on all or part of thesubstrate that cons the component or components and the conductivetracks in the vicinity.

The document EP0786357 describes a contactless card that comprises achip mounted on a substrate and connected to an antenna coil placed onthe edge of the substrate. The chip is placed in a substrate zonelocated on the exterior of the loop formed by the antenna coil in thevicinity of one of the edges of the card. This off-center position ofthe chip protects the latter against stresses caused by bending of thecard. The connection of the antenna coil to the chip is carried out byhot pressing the bumps of the chip contacts on the end tracks of thecoil. According to a variant this connection is achieved by soldering ofwires (“wire-bonding”) between the chip contacts and the tracks derivingfrom the coil.

The document US2002/0110955 describes a manufacturing method of anelectronic module comprising a substrate and at least one chip. Thelatter is either glued on one of the substrate faces, or hot pressedinside the substrate thickness in order to be level with the surface.Furthermore, the substrate includes conductive areas to which the chipis connected by means of conductive tracks made by silk-screening,according to a preferred variant. The chip contacts include bumps onwhich tracks, thus applied, end up to con the bumps. A final stepconsists in applying a thin film or a protection lacquer on the chip andon the conductive tracks located near the chip.

The transponders whose components are assembled according to the knownprocesses described above present a disadvantage at the level of qualityand reliability of the connection between the component and conductors.In fact, this connection can be interrupted totally or intermittentlydue to mechanical stresses applied to the transponder during its use.More particularly, the thin transponders such as cards or electroniclabels are easily deformable by flexion or twisting. These stresses canappear during the normal application of the transponder such as forexample on a label that is applied on the surface of an objectpresenting protrusions.

Despite the protection of the components by coating or lamination of aninsulating film, the connections of the components are subjected tointernal traction and compression causing their breakage when thetransponder is deformed. This phenomenon is further increased duringrepetitive deformations leading to the strain of the connection thatwill finally break after a few flexions or torsions suffered by thetransponder.

The aim of this invention is to avoid the drawbacks described above,namely to increase reliability and quality of the electric connectionbetween the electronic component or components and the substrateconductive tracks while reducing the manufacturing costs of thetransponder.

The aim of this invention is also to offer a manufacturing process forthis type of transponder in the form of a card or a label that iscapable of resisting flexions or twisting without interrupting componentconnections.

These aims are achieved by an assembly process of at least oneelectronic component including sensibly flat conductive areas that areconnected to conductive tracks placed on the surface of a generally flatinsulating support called a substrate characterized by the followingsteps:

-   -   placing the substrate on a work surface, the face including        conductive tracks being oriented upwards,    -   placing the electronic component into a cavity of the substrate        situated in a zone including the conductive tracks, the        conductive areas of the component coming into contact with the        corresponding tracks of the substrate,    -   applying a layer of insulating material which extends at the        same time on the component and at least on one substrate zone        surrounding said component, in such a way that the electric        connection between the conductive areas and conductive tracks is        ensured by the pressure of the insulating layer on the        component.

The electronic component also called the electronic module is usuallyformed by a chip whose contacts located on one of its faces are set offon a conductive film, called “lead frame” constituting contact areasthat extend the small dimensions of the chip contacts. In one embodimentexample, the opposite face of the chip is coated by an insulatingmaterial that is usually epoxy resin. The “lead frame” allows thefacilitation of the connection of the electronic module on theconductive tracks of a printed circuit. The majority of semi-conductivecomponents mounted on the surface of printed circuits include such “leadframes”.

The conductive tracks of the substrate are defined in an extensive way.They can be made up of pads or conductive areas connected to theconductive segments of a circuit engraved chemically or deposited bysilk-screening on the substrate. For example, this type of circuit canconstitute the antenna of a contactless card that serves to supplyenergy to the card and exchange digital data by means of a terminal.

It is important to note that the method according to the invention doesnot require any welding, nor any kind of anchoring of component contactson the circuit conductors. It is thus sufficient for the contactsurfaces of component and substrate to have been pressed one against theother by presenting approximately flat surfaces. The component isretained on the substrate by the insulating material covering the latterby extending on its periphery.

The cavity in the substrate is used to maintain temporarily thecomponent between its placing step and the depositing of the insulatinglayer. This cavity can be carried out by means of different ways such asmilling or cutting a window by stamping, or simply through thedeformation of the substrate by heating the component during its placingon the substrate.

The advantage of mounting the component according to this method residesin the fact that the contact between the component and the circuitconductor is maintained when the transponder is bent or twisted. Infact, the internal forces appearing at the level of connection tend tomake the contacts slide one on the other without producing any breakageas in the case of a welded or anchored connection. Repeated stressesexerted on the transponder cause a “self-cleaning” effect on theconductors by rubbing their surfaces together. Therefore, theperformance of the connection as well as its reliability and itselectric conductivity are greatly improved.

The invention will be better understood thanks to the following detaileddescription that refers to the enclosed drawings given as anon-limitative example, in which:

FIG. 1 represents a component in the form of an electronic moduleprovided with contact areas.

FIG. 2 represents an overview of a thin transponder comprising asubstrate and a component provided with contact areas protected by aninsulating layer

FIG. 3 shows an enlarged section of a the transponder in FIG. 2according to the axis A-A

FIG. 4 shows a section of a transponder assembly comprising twosubstrates and one component provided with contact areas

FIG. 5 shows a section of a transponder assembly comprising twosubstrates and one component made up of a chip inserted in one of thesubstrates.

The component (1) in FIG. 1 forming an electronic module includes a chip(2) protected by coating (4) in insulating material such as an epoxyresin. The chip contacts are connected to contact areas (3) formedinside a tinned copper conductive sheet, for example, forming the “leadframe”.

FIG. 2 and the section according to the illustrated axis A-A in FIG. 3show an example of a transponder that includes a thin substrate (5) thatcan be deformed on which the component (1) in FIG. 1 is placed. Theupper surface of said substrate includes tracks or conductive areas (6)engraved, glued or printed by silk-screening, for example. The coatedpart (4) of the component (1) is inserted into a cavity (7) made up ofmilling or a window cut into the substrate in order to minimize thefinal thickness of the transponder. The conductive tracks (6) of thesubstrate are in contact with the component conductive areas (3) only bymeans of pressure without using welding or conductive glue. Theapproximately flat surfaces in contact in this way do not include anyparticular type of relief serving as an anchorage point. The maintenanceof the component on the substrate and the pressure on its contacts areassured by an insulating layer (8) extended at the same time on thevisible surface of component and on a substrate zone in the vicinity ofthe component. According to a variant, this insulating layer can beextended on the whole upper surface of the substrate.

A transponder achieved in this way can be deformed without anyinterruption of component connections on the substrate conductors. Thecontact areas of the “lead frame” will have a tendency to rub on thesubstrate tracks under the action of internal forces produced by thetransponder deformation.

FIG. 4 shows a variant of the transponder assembly according to theinvention method, where the coated part (4) of the component (1) isinserted into a cavity or located in a window of a first insulatingsubstrate (5). The conductive areas (3) of the component are thusarranged on the lower surface of the substrate (5). A second substrate(9) that includes, on its upper surface, a plurality of conductivetracks such as for example an antenna (6′) and contact tracks (6)situated facing those of the component is applied on the first substrate(5). The assembly of two substrates (5, 9) is carried out by gluing orby hot or a cold lamination according to the arrows L. The electriccontact of the component with the tracks (6) of the second substrate isachieved by means of the lamination or gluing pressure. The finalthickness of the transponder is limited to that of the two superimposedsubstrates (5, 9).

According to another variant, the component (1) does not include acoating, the chip (2) is thus directly protected by the first substrate(5). The chip is either inserted into a cavity (7) that is pre-workedinto the substrate, or hot pressed into the substrate material in such away that the contact areas (3) of the component (1) are applied againstthe inner surface of substrate (5).

The direct insertion of the component into the substrate materialwithout a pre-worked cavity is carried out by heating the chip duringits placing that leads to the local softening and a deformation of thesubstrate. The chip is then pressed into the substrate by means of anadapted tooling to the desired depth. The cavity constituted in this wayis adapted to the chip outline and maintains the position of the chip orthe component assembly during the lamination of the second substrate.

The second substrate (9) is assembled in the same way as in the previousvariant. The thickness of the first substrate (5) can in this way bereduced to a value closer to that of the chip.

FIG. 5 represents a variant of the transponder assembly where thecomponent is made up by the chip (2) alone, free of “lead frame”. Inthis case, as in the previous one, the chip (2) is either housed in apre-worked cavity or pressed into the material of the first substrate(5) in such a way as to make its contact surfaces (3′) appear on thesubstrate surface (5) level. The second substrate (9) is provided withconductive tracks (6) facing those of the chip intended for itsconnection by means of the pressure of gluing or lamination of theassembly of the two substrates (5, 9). The contact surfaces (3′) of thechip (2) are of course flat allowing their friction on the correspondingconductive tracks of the second substrate in case of the transponderdeformation.

The insulating layer deposited on the component and on all or part ofthe surface of the substrate as well as on the second substratelaminated onto the first substrate can include a decoration or a markingon the external surface characterizing the final transponder. The firstsubstrate can furthermore also include decoration on the opposite sideto that supporting the conductive tracks.

The method according to the invention is also applied to the assembly ofcards called “dual” that is to say comprising on one hand a set of flatcontacts showing on the level of one of the external faces of the cardand on the other hand an internal antenna in the form of a set ofconductive tracks. This contacts set is placed on one of the faces of amodule and each contact is linked to a conductive area on the oppositeside of the module. The latter is inserted into a cavity provided with awindow cut into a first substrate whose thickness is approximately equalto that of the module. The contacts set shows on the surface level ofthe substrate constituting the external face of the card and theconductive areas of the opposite side lean against the conductive tracksof a second substrate assembled on the first substrate.

A chip or a supplementary electronic module as previously described,completing this assembly, can be mounted on either of the substrates.The conductive areas of this module are connected by pressure on thecorresponding conductive tracks of the surface of one of the substrates.

It is also possible to assemble and then laminate more than twosuperimposed substrates comprising conductive tracks and the electronicmodules whose conductive areas are connected by the lamination pressureto the corresponding conductive tracks arranged on the faces of eitherof the substrates.

1. Assembly process of at least one electronic component includingsensibly flat conductive areas that are connected to conductive tracksplaced on the surface of a generally flat insulating support called asubstrate characterized by the following steps: placing the substrate ona work surface, the face including conductive tracks being orientedupwards, placing the electronic component into a cavity of the substratesituated in a zone including the conductive tracks, the conductive areasof the component coming into contact with the corresponding tracks ofthe substrate, applying a layer of insulating material which extends atthe same time on the component and at least on a substrate zonesurrounding said component, in such a way that the electric connectionbetween the conductive areas and conductive tracks is ensured by thepressure of the insulating layer on the component.
 2. Process accordingto claim 1 wherein the electronic component is made up of a chipprovided with contacts on one of its faces, said contacts being set offon a conductive film constituting the contact areas that extend thecontacts of the chip, the opposite face of the chip being coated by aninsulating material.
 3. Process according to claim 1 wherein the layerof insulating material is made up of a first substrate including acavity into which the component is inserted by its coated face, thecontact areas of said component connecting with corresponding conductiveareas of a second substrate placed on the work surface.
 4. Processaccording to claim 1 wherein the electronic component is made up of achip provided with contacts on one of its faces, said contacts being setoff on a conductive film constituting the contact areas that extend thecontacts of the chip.
 5. Process according to claim 1 wherein theelectronic component is made up of a chip provided with contacts on oneof its faces, said contacts being set off on a conductive filmconstituting the contact areas that extend the contacts of the chip, thelayer of insulating material is made up of a first substrate including acavity in which the chip of the component is inserted, the contact areasof said component being applied against the surface of the substrateconnecting with corresponding conductive areas of a second substrateplaced on the work surface.
 6. Process according to claim 5 wherein thecavity of the component is obtained by heating the chip of the componentthen pushing said chip into the substrate material by means of adequatetooling, the contact areas of said component being applied against thesurface of the substrate (5).
 7. Process according to claim 1 whereinthe electronic component is made up of a chip provided with sensiblyflat contacts on one of its faces.
 8. Process according to claim 7wherein the layer of insulating material is made up of a first substrateincluding a cavity into which the chip is inserted, the contacts of saidchip showing on the surface level of the substrate are connected withcorresponding conductive areas of a second substrate placed on the worksurface.
 9. Process according to claim 1 wherein the cavity of thecomponent is made up by milling or by stamping a window.
 10. Processaccording to claim 8 wherein the cavity of the chip is obtained byheating then pressing said chip into the material of the substrate bymeans of adequate tooling, the contact areas of said chip showing on thesurface level of the substrate.
 11. Process according to claim 1 whereinthe electronic component is made up of a module including a set of flatcontacts on one of its faces and on the opposite face conductive areaslinked to each contact of the set.
 12. Process according to claim 1wherein the module is inserted into a cavity provided with a window cutinto a first substrate with a thickness approximately equal to that ofthe module, the set of flat contacts shows on the surface level of saidsubstrate and the conductive areas of the opposite face lean against theconductive tracks of a second substrate assembled on the firstsubstrate.
 13. Process according to claim 12, wherein at least onemodule or a supplementary chip is mounted in one of the substrates, saidmodule including conductive areas connected by pressure on thecorresponding conductive tracks of either of the substrates.
 14. Processaccording to claim 13 wherein it includes a supplementary step of gluingand pressing the assembly formed by the superposition of the substrates.